Selective hydrolysis of mixed organic acid esters of cellulose



Patented Feb. 16, 1937 UNITED STATES SELECTIVE HYDROLYSIS .OF MIXED OR-GANIC ACID ESTERS OF CELLULQSE William 0. Kenyon and Russel H. Van Dyke,

Rochester, N. Y., assignors, by mesne assignments, to Eastman KodakCompany, Jersey City, N. J., a corporation of New Jersey No Drawing.Application April 25, 1934, Serial No. 722,251

5 Claims.

The present invention relates to the regulation of the hydrolysis ofmixed organic acid esters of cellulose containing acetyl and higher acylgroups so that the relative rates of hydrolysis of the respective acetyland higher acyl groups may be varied with reference to each other.

One object of our invention is to provide a method of controlling theratio of the higher acyl groups to the acetyl groups, which may behydrolyzed off from a mixed organic acid ester of cellulose. Anotherobj-ect of our invention is to make possible the obtaining of producthaving the desired acetyl, higher acyl and hydroxyl contents.

The hydrolysis of mixed organic acid esters of cellulose whose acylcontent comprises at least of higher acyl is the invention of C. J. Malmand C. L. Fletcher and is disclosed and claimed in their applicationSerial No. 551,546 filed July 17, 1931. However, in the process whichthey describe the hydrolysis is induced merely by adding aqueous aceticacid to the reaction mixture. Thus the composition of that hydrolysisbath .depends on the proportion of ingredients employed in theesterification bath which in turn determines the acetyl and higher acylcontent of the ester formed so that the composition of the hydrolysisbath is related to the acetyl and higher acyl contents of the esterwhich is hydrolyzed when the hydrolysis is carried out by adding aqueousacid to the reaction mixture. For example it is not possible in aprocess in which hydrolysis is carried out by merely adding aqueousacetic acid to the reaction mixture containing the ester, to hydrolyzeoff a greater proportion of propionyl than acetyl groups from acellulose acetate propionate having a low percentage of acetyl,providing of course the starting material of the esterification'wascellulose per so due to the fact that the proportion of propionyl andbutyryl groups to the total acyl content of the bath determines the acylratio of the resulting ester. Thus the bath in which the celluloseacetate propionate having a low acetyl content is produced has apredominant amount of propionyl. groups therein and even though diluteacetic acid is added thereto the acetyl groups will be hydrolyzed offthe more rapidly as the bath is predominantly propionyl. Likewise it isnot possible by that method, to hydrolyze off the acetyl groups ingreater amount than the propionyl groups from a cellulose acetatepropionate in which the acetyl predominates.

We have found that if a cellulose acetate-higher acylate is subjected tothe hydrolyzing action of aceticacid and water that the higher acylgroups will hydrolyze off more rapidly than the acetyl while on theother hand if the ester is subjected to the action of a hydrolyzing bathcomprising propionic or butyric as the predominant acid present andwater, the acetyl groups will hydrolyze oft (Cl. 260102) g more rapidlythan the higher acyl groups;

have found that starting from a single mixed ester of cellulose such asa cellulose acetate propionate or acetate butyrate, hydrolyzed productshaving varying contents of acetyl and higher acyl groups may beobtained.

Our invention may be carried out by treating a mixed organic acid est-erof cellulose containing acetyl groups in solid form with a hydroly'zingbath comprising acetic or the higher acid corresponding to the higheracyl of the ester, (where that higher acid is compatible with the otheringredients of the bath) or a mixture of the acetic with at' least oneof the higher acids in me do sired proportions according to thecomposition. desired in the resulting product... In cases where;

the cellulose ester is in solution in one or the other or a mixture ofthese acids the presentingvention is also applicable, as whentheester-is in solid form it"must be dissolved'before'the hy acid up to themaximum amount compatible. therein, are within the contemplation of the"invention. 1

The following examples illustrate processes of hydrolyzing a mixedester, of cellulose, containing acetyl and higher acyl groups, embodyingth'e present invention:

Example I V 95 lbs. of cellulose acetate propionate were dissolved in470 lbs. of glacial acetic acidand a hydrolyzing mixture consisting of42 lbs. of glacial acetic acid, 26 lbs. of Water and 2.3 lbs. of

sodium bisulfate monohydrate was added thereto. The whole was maintainedat 53 C. and samples were removed at intervals. These were precipitated,washed and dried and were ana lyzed as indicated below:

Percent of acyl groups Percent based on total acyl Time of hydrolysis(hrs) apparent j acetyl Acetyl Propionyl It will be noted that at firstthe propionyl content gains at the expense of the acetyl. Al-

though it has been recognized that in the hy-- drolysis of celluloseacetate, during the first part 7 of the process, the acetyl contentincreases if an increase in acetyl content is possible, however inthat-case acetic acid is present in the bath.

The present phenomena can hardly be considered analogous thereto andwith the present state of the art it does not appear that an explanationtherefor is forthcoming. It will be noted that in Example II a similarphenomena occurred except that the conditions were the converse of thosein Example I.

Example II Percent of acyl groups Percent based on total acyl apparentTime of hydrolysis (hrs.)

' acetyl Acetyl Propionyl Example III 95 lbs. of cellulose acetatepropionate were dissolved in a mixture consisting of 345 lbs. ofpropionic acid, 55.5 lbs. of 99% acetic anhydride and 55.5 lbs. ofglacial acetic acid. 'A hydrolizing mixture consisting of 42 lbs. ofglacial acetic acid, 26 lbs. of water, 2.3 lbs. of sodium bisulfatemono- D hydrate and 3 lbs. of a mixed catalyst consisting of 1 part byvolume of sulfuric acid and 3 parts by volume of phosphoric acid wasadded thereto and the whole was maintained at a temperature of 53 C.Samples were removed and analyzed 5 Example IV I 95 lbs. of celluloseacetate propionate were dissolved in 470 lbs. of glacial acetic acid anda hydrolyzing mixture consisting of 42 lbs. of glacial 'bisulfatemonohydrate and 3.7 lbs.;of mixed catalyst (1 part byvolume of sulfuricto 3 parts by. volume of phosphoric acid) was added thereto. Theresulting mixture was maintained at a tem- 7 perature of 53f C(andsamples were removed acetic acid, 26 lbs. of water, 2.3 lbs. of sodiumintervals and theester therein precipitated out, washed, dried andanalyzed with the following results:

. Percent of acyl groups 7 Percent based on total acyl Time ofhydrolysis (hrs) apparent acetyl Acetyl propionyl Emample V Percent ofacyl groups Percent based on total acyl Time of hydrolysis (hrs.)apparent acetyl Acetyl Propionyl Example VI 100 lbs. of celluloseacetate butyrate were dissolved in 472 lbs. of acetic acid and a mixtureconsisting of 42 lbs. of glacial acetic acid, 26 lbs. of water, 2.3 lbs.of sodium bisulfate monohydrate and 3.7 lbs. of the sulfuric-phosphoriccatalyst was added thereto. The mass was maintained at 53 C.,.andsamples were removed atzintervals, the ester therein being precipitatedout, washed, dried and analyzed with the following resultsz Percent ofacyl groups Percent based on total acyl Time of hydrolysis (hrs.)apparent acetyl Acetyl Butyryl Example VII 7 Percent of acyl groupsPercent based on total acyl Time of hydrolysis (hi-s.) apparent acetylAcetyl Butyryl It is to be noted in Example III the hydrolysis wascarried out in a mixture of acetic and propionic acids, however due tothe fact that the amount of propionic acid predominates the acetylgroups were hydrolyzed oif more rapidly than the propionyl groups. It isalso to be noted that the hydrolysis in this example proceeded morerapidly than in the hydrolysis of Example II which was due to thepresence of mineral acids therein. The effect the proportion of sulfuricacid to the cellulose in the hydrolysis bath exerts on the speed of thehydrolysis is the discovery of C. J. Malm and C. L. Fletcher and isdisclosed and claimed in their application Serial No. 651,138. Due tothe fact that a mixture of acetic and propionic acids was employed inExample III, the acetyl groups were not hydrolyzed off as rapidly inproportion to the apparent acetyl content as was the case in Example IIin which propionic acid only was employed.

Example VIII The present invention is applicable to the hydrolysis ofthe esters the higher acyl of which corresponds to an organic acid whichis compatible in but a small proportion with the hydrolyzing bath,however, due to this fact the use of a hydrolyzing bath substantiallycomprising the higher acid is not possible. However, the relativehydrolysis of the respective groups can be governed between the limitsof hydrolyzing baths in which acetic is the sole organic acid presentand in which the highest percentage of the higher acid compatible withthe hydrolyzing bath is present. 500 gms. of a cellulose acetatestearate having an acetyl content of 26.5% and a stearyl content of 37.7is completely dispersed at 25 C. in 4 liters of glacial acetic acid. Tothis dispersion is added the following mixture to hydrolyze the ester:

2 l. glacial acetic acid 12 gms. sodium bisulfate monohydrate 130 cc.water cc. of a catalyst consisting of a mixture of 1 part of sulfuricacid and 3 parts of phosphoric acid by volume. The whole is agitated torender it homogeneous and it may be placed in an environment having atemperature of 50-55" C. Samples may be removed at intervals,precipitated and washed with methyl alcohol, washed with ether, driedand analyzed. The following results are obtained:

P Ratio of Time of hydrolysis (hrs.) 2%??? 5 :5 2 ggg groups Example IX400 gms. of a cellulose acetate phthalate having an acetyl content of23.4% and a phthalyl' content of 20.6% is dissolved in 2 l. of glacialacetic acid and hydrolyzed at 50-55 C. by adding the follow inghydrolyzing mixture:

200 cc. glacial acetic acid 120 gms. sodium bisulfate monohydrate 130cc. water I 10 cc. of sulfuric-phosphoric acid catalyst (1 part H2SO4 to3 parts H3P04 b volume).

Samples may-be removed at selected time intervals, precipitated andwashed in distilled .water until the wash water shows no acidity. Uponanalysis the following results are obtained:

Ratio of phthalyl to acetyl groups Percent phthalyl Percent Ratio 0!Percent phthalyl Percent Time of hydrolysis (hrs) acetyl groups Some ofthe phenomena observed is inexplicable however it is apparent that thepresence of the higher acid in each case causes the ratio of higher acylto acetyl groups in the ester to increase more than is the case wherethat higher acid is absent. It might be presumed from the above resultsthat the analysis was rather inaccurate however such is not necessarilythe case as in view of our knowledge of the variations which may occurin the acetyl content of a celphthalyl to U lulose acetate during itshydrolysis it seems reasonable to presume that this variation isinherent in the particular hydrolysis in which it occurs.

It is to be understood that the rate of removal of the acyl groups willvary in accordance with various conditions. As shown in Example III,when the mineral acid content of the hydrolysis bath is increased, otherthings being equal, the speed of hydrolysis is also increased. When thetemperature of the bath is lowered the rate of hydrolysis is decreasedand upon increase of temperature the hydrolysis rate is increasedalthough danger from degradation of cellulose presents itself at toohigh a temperature. Nevertheless in any given hydrolysis bath therelative rate at which the acetyl and the higher acyl groups arehydrolyzed off may beregulated by adjusting the relative proportions ofacetic and higher acid acetyl and acyl groups of- 3-4 carbon atoms whichcomprises partially hydrolyzing the ester' 7 acid employed in the'hydrolyzing bath.

2. A processionhydrolyzing mixed monocarboxylic acid esters of cellulosecontaining both acetyl and acyl groups of 3-4 carbon atoms whichcomprises partially hydrolyzing the ester in a bath essentiallyconsisting of water, catalyst and acetic acid, thereby removing acylgroups of 3-4 carbon atoms from the cellulose'ester.

; 3; A process for hydrolyzing cellulose acetate propionates whichcomprises partially hydrolyzing the ester in a bath essentiallyconsisting of water, catalyst and acetic acid, thereby removingpropionyl groups from the ester.

4. A process for hydrolyzing cellulose acetate propionate whichcomprises partially hydrolyzing'that ester in a bath essentiallyconsisting of water, catalyst and propionic acid, thereby removingacetyl groups from the cellulose ester.

5. A process for hydrolyzing cellulose acetate 'butyrate which comprisespartially hydrolyzing the ester in a bath essentially consisting ofwater, i

catalyst and butyric acid, thereby removing acetyl groups from theester. s I

WILLIAM O. KENYON.

RUSSEL H. VAN DYKE.

